Process for making variable denier yarn



United States Patent 3,363,295 PROCESS FOR MAKING VARIABLE DENIER YARN Frederick Clifford Allen, Abergavenny, England, assignor to British Nylon Spinners Limited, Pontypool, Monmouthshire, England, a corporation of Great Britain No Drawing. Filed Sept. 27, 1965, Ser. No. 490,686 Claims priority, application Great Britain, Oct. 21, 1964, 42,933/ 64 3 Claims. (Cl. 2875) ABSTRACT OF THE DISCLOSURE Variable denier yarn of nylon or polyethylene terephthalate is continuously produced by a drawing process in which a localized draw point in the yarn between feed rolls and draw rolls migrates in the direction of yarn advance so that new draw points are repeatedly formed in the advancing yarn with the result that the yarn has relatively undrawn regions alternating with relatively drawn regions. This effect is obtained by employing a mechanical draw ratio which is less than the natural draw ratio of the yarn and by employing a second drawing step in which the mechanical draw ratio is low enough to prevent yarn breakage.

The present invention relates to coloured nylon or polyethylene terephthalate yarns and fabric made up therefrom.

Methods have been described in patent specifications published during the past decade in which nylon or polyethylene terephthalate yarn is drawn under such conditions as to result in a yarn of variable denier and, hence, variable dyeing capacity when dyes are used whose degree of up-take varies with the degree of molecular orientation in the polymer being dyed.

When such yarns are woven or knitted into fabric and the yarn is dyed with a dye of the above-mentioned kind, the result is a mottled multiple-tone fabric of pleasing appearance. If desired, the resultant multiple-tone fabric may be subjected to a further dyeing operation using a disperse dye of some different colour. Disperse dyestuffs are substantially insensitive to differences in molecular orientation in the polymer and the result may then be a multiple-coloured fabric.

Three methods for forming such yarns that have already been proposed are described in British patent specifications Nos. 812,110, 822,706 and 917,453, respectively. In brief, the first method relies upon the effect of heating alternate regions of an undrawn yarn to different extents before drawing, the more heated regions of the yarn then drawing to a greater extent than the lesser heated or unheated regions. The second method relies upon the effect produced by varying in periodic fashion the length of yarn etween the feed roll(s) and the draw roll(s) of a drawing machine; and the third method relies upon the effect of applying to the undrawn yarn a crack-promoting agent, the effect of which is to create at random along the length of the undrawn yarn points of weakness at which drawing is preferentially initiated.

The present invention provides a further method of forming yarns having lesser-drawn regions alternating with more-drawn regions, whch method comprises subjecting a yarn formed of nylon or polyethylene terephthalate to a first drawing operation in which the mechanical draw ratio is less than the natural draw ratio of the yarn at the drawing temperature so that, repeatedly, a localised drawing point or nec is formed along the length of the yarn at which the denier falls off with distance in the direction of advance of the yarn and that migrates in the direction in which the yarn is advancing, then subjecting yarn Withdrawn from the first drawing operation which has relatively undrawn regions alternating with relatively drawn regions to a second drawing operation in which the mechanical draw ratio is sufficiently low for the numerical product of the second mechanical draw ratio and the natural draw ratio of the yarn at the temperature of the first drawing operation to be less than the draw ratio of the yarn at break, and dyeing the resultant yarn with a dye that is sensitive to differences in the degree of molecular orientation in the yarn polymer.

The invention also provides a fabric of multiple-tone mottled appearance woven or knitted of yarn made by the method of the invention. If desired, the multiple-tone fabric may be post-dyed with a disperse dye so as to form a multiple shade or colour fabric.

The terms natural draw ratio and mechanical draw ratio are well understood in the art but a brief explanation here of their meanings may perhaps assist. The mechanical draw ratio is the ratio of the lineal speeds at which the yarn is supplied to and withdrawn from the zone in which drawing occurs. Thus, where the customary form of drawing apparatus is used, it is the ratio of the peripheral speeds of the forward draw roll(s) and the feed roll(s) of the drawing apparatus. The mechanical draw ratio is, therefore, a function of the working parameters only. The natural draw ratio, on the other hand, is characteristic of the yarn. When, for example, nylon yarn is drawn, a localised draw point or neck tends readily to form and normally will be formed. At the neck the denier of the yarns falls off very rapidly with distance in the direction of advance of the yarn and the draw ratio at the neck is the ratio of the cross-sectional areas of the yarn immediately on opposite sides of the neck. It is surprisingly found that the draw ratio across the neck is substantially constant for a given state of orientation in the undrawn yarn and a given yarn temperature no matter what the denier of the yarn drawn or the mechanical draw ratio of the drawing apparatus, and, for that reason, it is termed the natural draw ratio. Where yarn to be subjected to the first drawing operation has been spun under conditions favourable to the occurrence of yarn polymer orientation, the employment of a relatively low first drawing temperature may be neces sary in order to ensure that a neck shall form during the first drawing operation.

In normal drawing every effort is made to ensure that the drawing point or neck remains stationary. If the mechanical drawing ratio exceeds the natural draw ratio, the drawing point or neck moves towards the feed roll(s) unless prevented from doing so by some device. In practice, a snubber pin is used to locate the drawing point. As is well known, the snubber pin provides a tension barrier preventing migration of the neck towards the feed roll(s) because the tension in the yarn in advance of the snubber pin is always kept so low that it is impossible for a neck to form or be stabilised in advance of the snubber pin. The yarn is allowed to reach the minimum tension necessary for neck formation only when it is passing around the periphery of the snubber pin.

In the first drawing operation of the method of the invention, the drawn yarn is withdrawn at a lesser rate (mass/unit time) than that at which it is supplied. In other words, the drawn yarn is withdrawn at a speed that is less than the numerical product of the natural draw ratio and the speed at which the undrawn yarn is supplied. The necessary consequence is that the draw point or neck migrates to the forward draw roll(s).

Normal drawing apparatus having feed roll(s), draw roll(s), and a snubber pin is preferred for use in carrying out the drawing operations in the method of the invention and it will be realised that the distance between the snubber pin and the forward draw roll(s) places an upper limit on the possible lengths of the regions of undrawn yarn in the yarn withdrawn from the first drawing operation. The regions of undrawn yarn that remain after the first drawing operation will, in general, vary considerably in length and in almost random fashion because, where the yarn and working conditions are uniform over the whole yarn path between the snubber pin and the forward draw roll(s), no one intervening spacial position is preferred to another for the re-formation of a draw point and a draw point or, indeed, any of a number of draw 3 points may be formed at any intervening position.

Precisely what takes place in the second drawing opera tion is not fully understood at this time, but the second drawing operation is considered essential for the formation of acceptably dyed yarn and fabric made up therefrom. If the second drawing stage is dispensed with and the yarn that is withdrawn from the first drawing operation is made up into a fabric and dyed, the result is a fabric of patchy coarse appearance with too much contrast in colour intensity between neighbouring portions of the fabric. The second drawing operation appears to be essential for forming a fabric of more refined appearance in which the colour shades or tones tend to blend one into another and none of the shades stands out in stark relief against the ground. A preliminary study of the colour shades obtained on dyeing fabrics made up of yarn prepared by the method of the invention indicates (insofar as shade intensity can give an approximate guide to degree of molecular orientation and hence degree of drawing) that certain regions of the yarn remain substantially undrawn despite the second drawing operation, while other regions of the yarn appear to be drawn only to a draw ratio less than the natural draw ratio. This suggests. that drawing accompanied by necking, and at the natural draw ratio, as well as drawing unaccompanied by necking, and at a draw ratio less than the natural draw ratio, occur during the second drawing operation, in addition to some further drawing of yarn that has already been drawn to the natural draw ratio in the first drawing operation.

Unless the dimensions of the apparatus used for the second drawing operation are very large relative to those of the apparatus used for the first drawing operation, there is a distinct possibility that at some moments during the second drawing operation the apparatus will be drawing yarn that has already been drawn as a whole to the natural draw ratio. Any attempt to draw such yarn more than a modest amount will be likely to result in yarn breakage. Where, however, as in the method of the invention, the product of the natural draw ratio at the first drawing temperature and the mechanical draw ratio of the second drawing operation is less than the draw ratio of the yarn at break, yarn breakage is unlikely to occur.

It is not a diflicult task to arrive at suitable values for the draw ratios for the first and second drawing operations and to set up apparatus for carrying out the method of the invention, and, while the exact effects of varying the mechanical and natural draw ratios and the lengths of yarn in the drawing zone of the two drawing operations on the appearance of the resultant dyed yarn and fabric cannot at this time be predicted with certainty, it is a matter for relatively simple experiment to try the eifect of such variations. 7

It has also been found that yarn made by the method of the invention or by a modification of that method in which :a disperse dye is used instead of a dye that is sensitive to difference in molecular orientation can be used with advantage in forming the pile of carpets. Carpets, and especially looped-pile carpets, of which the pile is wholly or mainly formed of such yarn have noticeably enhanced surface sparkle and reflectivity when compared with yarn of constant denier but otherwise equivalent characteristics. This is presumably because the yarns made by the method of the present invention or its aforementioned modification have regions along their lengths that can focus directional incident light. Where there is a pattern in relief on the surface of the looped-pile carpet and the carpet surface is illuminated by obliquely directed incident light (as from a window) the relief pattern is optically more pronounced when the present'variable denier yarn is used instead of an equivalent yarn of constant denier.

The following examples illustrate the invention:

210 denier, 34 filament (210/ 34) nylon 6.6 yarn that had been melt-spun at a speed of 1,200 ft./min. and conditioned in a steam atmosphere was subjected to twostage drawing employing standard drawing apparatus comprising feed rolls, a snubber pin, and forwarding draw rolls. The atmosphere in which drawing took place was at a temperature of 23 C. and had a relative humidity of 67%. For convenience, the two drawing operations were carried out consecutively on the same drawing apparatus instead of on apparatus capable of effecting two drawing operations in sequence without intervening windup of yarns, and the distance between the snubber pin and the forward draw rolls was kept at 12.5 inches. For both drawing operations, thespeed at which the yarn was supplied to the drawing zone was 350 ft./min. so that the rate of revolution of only the forward draw rolls had to be changed from one drawing operation to the next in order to adjust the mechanical draw ratio to the desired value.

Five runs with different combinations of 1st and 2nd mechanical draw ratios were carried out and the product of the 1st and 2nd mechanical draw ratios for each run was substantially equal to 4.

The values of the mechanical draw ratios for the 1st and 2nd drawing operations of each of the five runs are listed in the following table:

Run No. 1st Mechanical 2nd Mechanical Draw Ratio Draw Ratio the result was a yarn of varying depth of colour over.

portions of varying length. A knitted fabric made up from the yarn appeared, when looked at not too closely, to be two-tone, with dark blue regions spaced apart'by light blue regions. Close inspection, however, revealed that regions of intermediate colour were present also which tended to soften the outline of the darker blue regions.

The most balanced fabric, and the one which we preferred, was obtained from the yarn that resulted from run No. 3 and it was, in overall appearance, essentially two-tone with deep blue bars of shorter and greater length, on a light blue ground. The deep blue bars were well defined without standing in stark relief against the light blue ground.

On close inspection, regions of intermediate depth of colour shade were seen to be present, and to be responsible for softening the outline of the deeper blue bars. Fabrics knitted from the yarns resulting from runs Nos. 1 and 5 were predominantly of one colour shade and such regions as there were of a different shade imparted to the fabric a blotchy and smudgy appearance.

Further samples of the yarn resulting from runs Nos. 2 and 3 were formed into carpet yam of 1040 denier, 68 filaments and 0.7 turns per inch were dyed with a blue disperse dye, and used to form looped-pile carpets with a sculptured diamond pattern on the pile surface. A sample of carpet was made up which was equivalent in all respects except that as yarn there was employed a yarn of comparable but uniform denier. The carpet samples made up of the yarns resulting from runs No. 2 and 3 had a pleasing appearance and considerable surface sparkle but they differed one from the other slightly in overall appearance probably due to the different light reflecting properties of their surfaces.

The relief pattern was pleasing in each case when viewed under obliquely incident light. The comparison sample, on the other hand, had a uniform sheen, was accordingly somewhat lifeless, and the sculptured pattern was here not as plainly visible as in the other two cases.

What 'I claim is:

1. A method of forming yarns having lesser-drawn regions alternating with more-drawn regions, which method is characterised by the steps of subjecting a yarn selected from the group consisting of nylon yarn and polyethylene terephthalate yarn to a first drawing operation in which the mechanical draw ratio is less than the natural draw ratio of the yarn at the drawing temperature so that, repeatedly, a localised drawing point or neck is formed along the length of the yarn at which the denier falls off with distance in the direction of advance of the yarn and that migrates in the direction in which the yarn is advancing whereby that portion of the yarn which follows the localized drawing point out of said drawing operation will be relatively undrawn, and then subjecting yarn withdrawn from the first drawing operation which has relatively undrawn regions alternating with relatively drawn regions to a second drawing operation in which the dnaw ratio is sufficiently low to prevent excessive yarn breakage.

2. A method as claimed in claim 1 wherein the yarn from the second drawing operation is dyed with a dye 6 that is sensitive to differences in the degree of molecular orientation in the yarn polymer.

3. A method of forming yarns selected from the group consisting of nylon yarn and polyethylene terephthalate yarns into yarns having lesser-drawn regions alternating with more drawn regions comprising: advancing the yarn continuously at generally constant speed into a drawing zone, applying drawing tension to the yarn in said zone and continuously withdrawing the yarn irom said zone at a generally constant speed such that the mechanical draw ratio is less than the natural draw ratio of the yarn at the drawing temperature so that a localized drawing point is formed repeatedly in the yarn and advances with the yarn and passes out of said zone whereby that portion of the yarn which follows the localized point out of said zone will be relatively undrawn; and then subjecting the yarn withdrawn from the first drawing operation which has relatively undrawn regions alternating with relatively drawn regions to a second drawing operation in which the mechanical draw ratio is sufiiciently low for the numerical product of the second mechanical draw ratio and the natural draw ratio of the yarn at the temperature of the first drawing operation to be less than the draw ratio of the yarn at break so as to prevent breakage of the yarn in the second drawing operation.

References Cited UNITED STATES PATENTS 3,124,632 3/1964 Larkin et a1. 264290 3,212,158 10/1965 Kasey 28-74 LOUIS K. RIMRODT, Primary Examiner. 

